Circuit interrupter



May 16, 1950 T. LINDsTRoM ETAL CIRCUIT INTERRUPTER Filed Feb. 1o, 1944Patented May 18, 1950 CIRCUIT lNmRUPTEB Ture Lindstrom, E

and Bernard G.

dwmd, Tremblay, Wilkinslmrg, Pa., asslgnors to Westinghouse ElectricCorporation, East Pittsburgh,

Pa., a corporation of Pennsylvania Application February 1I, 1944, SerialNo. 521,788

(Cl. 20o-103) iz claim. l

This invention relates to circuit interrupters and more particularly tocircuit interrupters embodying electromagnetic tripping means fortripping the interrupter in response to overloads above a predeterminedvalue.

An object of the invention is to provide a circuit interrupter havinginstantaneous and time delay trip mechanism with improved means foradjust- `ing the instantaneous tripping characteristics of theinterrupter.

Another object of the invention is to provide a circuit interrupter withan improved electromagnetic trip means having an armature and a fixedcore wherein a portion of the magnetic core is adjustable relative tothe armature to vary the tripping characteristic of the electromagnet.

Another object of the invention is to provide an improved circuitinterrupter with a novel electromagnetic trip device, the electromagnethaving an armature and two magnetic flux circuits and corresponding airgaps disposed to produce a differential pull on the armature, theminimum tripping current required to instantaneously trip theinterrupter being determined by varying the differential pull of themagnet.

Another 'object of the invention is the provision of a circuitinterrupter with a novel electromagnetic tri-p means comprising anarmature and xed and movable core members for producing a differentialpull on the armature, said movable core member being manuallyradjustable to vary the differential pull of the electromagnet.

Another object of the invention is the provision of a circuitinterrupter with an improved electromagnet and trip device comprising anarmature and a fixed core structure disposed to produce a differentialpull on said armature, at least a part of the fixed core structure beingadjustable relative to said armature to vary the differential -pull ofthe electromagnet to thereby adjust the tripping characteristic of thedevice.

Another object of the invention is the provision of a circuitinterrupter with an electromagnetic trip device having a plurality ofparallel magnetic flux circuits and adjustable means to vary the minimumcurrent value for instantaneously tripping the interrupter.

The novel features that are considered characteristic of the inventionare set forth in particular in the appended claims. The inventionitself, however, both as to structure and operation, together withadditional objects and advantages thereof, will be best understood fromthe following detailed description thereof when read in t achannel-shaped switch arm 23.

conjunction with the accompanying drawings, in which:

Figure 1 is a vertical sectional view ofA a circuit breaker embodyingthe invention;

Fig. 2 is a vertical sectional view on an enlarged scale of the tripdevice;

Fig. 3 is a bottom view of the electromagnetic trip devices for twoadjacent poles of the interrupter with the trip device cover partlybroken away to show the adjustment of the adjustable core member; and

Fig. 4 is a detailed sectional view taken on the line IV-IV of Fig. 3and showing the method of mounting the fixed and adjustable coremembers.

Referring to Fig. 1 of the drawing, the circuit interrupter is of thethree pole type and comprises a base l of molded insulating material,`

a cover 9 also o! molded insulating material secured to the base bymeans of bolts (not shown) operating mechanism indicated generally at Iland a trip device indicated generally at I3 having a separateelectroresponsive tripping means for each of at least two of the polesof the interrupterl Each pole of the breaker is provided with astationary contact I5 mounted on the lower end of a conductor I1 of thecorresponding pole of the breaker, the conductor being suitably securedto the base 1.

The movable contact structures of the several poles are the saine, forwhich reason only the movable contact structure for the center pole hasbeen shown and will be described. 'I'he movable contact I9 for thecenter pole is secured to a contact arm 2| which is loosely supported onThe three channel-shaped switch arms of the three poles are rigidlyfastened for unitary movement by means of a metal tie bar 25 whichextends transversely across all of the poles of the breaker. The tie bar25 is fastened to the switch arms 23 adjacent the pivoted ends thereofby means of metal straps 2l looped about the tie bar and clinchedthereagainst. The tie bar is surrounded by an insulating tube 29 inorder to insulate and prevent short circuiting of the poles of theinterrupter. By means of the tie bar 25, al1 of the switch arms 23 aremechanically interconnected so that all three of the switch arms areoperated by a single operating mechanism, which is hereinafterdescribed. The channel-shaped switch arm 23 for the center pole ispivotally supported on a pin 3| mounted in a U-shaped main frame 33secured to the base 'l by means of screws 35. The pivot pinl forms the'common pivot for the three mechanically connected switch arms 2l.

Each of the contact arms 2|, to which the movable contacts I9 aresecured, is attached to its corresponding channel-shaped switch arm 23by means oi' a headed adjusting bolt 31 which threadedly engages theswitch arm and is locked in adjusted position by a lock nut 39. The head(not shown) ofthe bolt 31 loosely engages in a recess in the contact armand is retained therein by an inwardly iianged portion of the contactarm. Contact pressure is provided by a compression spring 4I having oneend seated in a cup-shaped spring seat 43 mounted on the switch arm 23near its upper end and the other end bearing against the contact arm 2|.The spring 4I, in the open contact position of the switch arm 23, biasesthe contact arm 2| counterclockwise about the head of the bolt 31, themovement being limited by a tail portion of the contact arm 2| strikingthe channel-shaped switch arm 23.

The upper end oi' a iiexible conductor 45 is electrically andmechanically connected to the 4 portion of the operating lever isprovided with a formed over portion 39. The portion 99 of the operatinglever is for the purpose'o! engaging and resetting the carrier 59 to itslatched position by movement of the operating handle as far as it willgo in opening direction, in order to reset the mechanism following atripping operation of the interrupter. The' carrier' 59 is normallyrestrained in latched position as shown in Fig. l by a latch 9I of thetrip device, which engages a latching portion 93 of the carrier.

lower end of the contact arm 2| by means oi' a clamp 41 and the lowerend of the flexible conductor is connected by means of a screw 49 to aconductor (Figs. 2, 3 and 4) which forms the energizing means for thecorresponding pole of the trip device I3. The conductor 5| has its lowerend connected by means of a bolt 53 and nuts 55 to a terminal connector51. The upper end of the conductor I1 is similarly connected to aterminal connection (not shown) but similar to the connector 51. Thecircuits for the two outer poles are the same as the circuit for thecenter pole, consequently, only the circuit for the center pole will betraced. This circuit extends from the upper terminal (not shown) throughthe conductor I1, stationary contact i5, movable contact I9, contact arm2|, flexible conductor 45, the trip device I3 energizing conductor 5Iand the bolt 53 to the terminal connector 51.

The movable contact structure comprising the channel-shaped switch arms23, the tie bar 25 and the contact arms 2| for all three poles of -thebreaker, is adapted to be operated to open and closed positions to openand close the circuit of the interruptor by the single operatingmechanism II. This operating mechanism comprises a carrier or supportmem-ber 59 pivotally mounted by means of a pin 6| on the main-frame 33,a pair of toggle links 93 and 95 interconnecting the carrier 59 and thecenter pole switch arm 23, a U-shaped operating lever 91, overcentersprings 69 for connecting the operating lever 51 to the knee pivot pin1| oi' the toggle links -63 and 65, and an insulating operating handle13 for the operating lever.

The toggle link 63 is pivotally connected by means of a pin to thecarrier 59, while the toggle link 65 is pivotally connected by means ofa pin 11 to the channel-shaped switch arm 23 for -the center pole of theinterrupter. The two legs of the operating lever 61 are disposedadjacent the inner sides of the main frame 33 and are pivotallysupported on pins 19 projecting inwardly from the sides of the frame.The operating handle 13 projects through an opening 8| in the cover 9and has an arcuate protective portion 83 having ,side portions 85integral with the portion 93. The side portions 95 of the operatinghandle straddle the main frame 33 and are secured to the two legs of theoperating lever 91 by means of screws 81 which threadedly engage therespective legs of the operating lever 61. The connecting The operationof the circuit interrupter operating mechanism is 'as follows: with theparts in the position shown in Fig. 1, in which position all of thecontact means are closed and the carrier 59 is held in latched position;if the operating handle 13 is moved in a clockwise direction from theposition shown to the opposite end of the slot 8| thus rotating theoperating lever 61 in a clockwise direction, the overcenter spring 69will snap overcenter below the linef`H-15 and cause the toggle links63--65 to collapse, thereby causing simultaneous movement of all of thechannelshaped switch arms 23 and the movable contacts I9 to theopen-circuit position with a snap action. To reclose the interrupter,the operating handle is moved in the opposite direction back to theposition shown in Fig. 1. This movement of the handle causes theovercenter springs to snap overcenter in the opposite direction and movethe toggle to the in-toggle position to simultaneously close all of thecontact means with a snap action.

The circuit interrupter is opened automatically in response to overloadcurrents occurring in the -circuit of any pole of the breaker, byoperation of the trip device I3. When the latch 9| is released by thetrip device in response to an overload current, it frees the carrier 59and permits the springs 69 to rotate the carrier in a counter-clockwisedirection, thus causing collapse of the toggle 53-65 and movement of thechannel shaped switch arms and the movable contacts for all three polesof the breaker to the open circuit position. The breaker cannot beclosed after a tripping operation until the handle is moved to the fullyopened position in order to reset and relatch the carrier 59 with thelatch 9|. After the carrier has been relatcheld, the operating Vhandlemay then be moved to the closed circuit position to eiect closing of thecontacts.

The trip' device comprises an insulating base or support member 95 (Fig.2) secured by means of rivets 91 or other suitable means to an anglebracket 99 which is, in turn, secured to the base 1 of the interrupterby means of the screws 49. A cover |00 of insulating material enclosesthe trip device. The electroresponsive tripping means for the-threepoles are the same, therefore only the one for the center pole will bedescribed. The energizing conductor 5| of each pole has a loop IBItherein, the upper leg of the loop being disposed adjacent to the base95 and secured by means of a screw |03 to the underside of the base 95.A bimetal element |05 has one end secured by means of rivets |01 orother suitable means to the lower leg'of the loop near the base of theloop. The rivets |01 also serve to rigidly secure both the lower loop ofthe heater element 5| andthe bimetal element |05 to a support bracket||9 to which is also secured the electromagnetic trip means to be laterdescribed.

The bimetal element |05 extends toward the right (Fig. 2) substantiallyparallel to and adjacent the lower leg of the loop |0I. The free end ofthe bimetal is'disposed adjacent Yan adjusting screw |05 mounted in aninsulating trip bar III. The trip bar is pivotally mounted by Pins Il!-supported in the trip bar engaging bearing projec tions ||5 (Fig. 3)extending downwardly from the bracket 39 through openings (not shown) inthe base 95. In the normal position of the trip bar a latch member ||2(Fig. 2) thereon engages a latch portion ||4 of the latch member 3| torestrain this latch in latching position. When the bimetal element |05is heated a predetermined amount in response to overload currents, itderiects downwardly to engage the adjusting vscrew |09 and rocks thetrip bar clockwise about magnetic means for each of at least two of thepoles of the breaker operable in response to overloads above apredetermined value, or in response to short circuits to instantaneouslyactuate the trip bar I to trip the interrupter. Each electromagnetcomprises a iixed U-shaped core member I |1 (Figs. 2 and 3) iixedlymounted on the bracket H9, a movable U-shaped core member |23, andanarmature |25. The bracket ||9 is of non-magnetic material and issecured to spaced projections |2| (Fig. 4) integral with the base 85.

The iixed core member I |1 and the bracket Il! are rigidly mounted onthe projections I 2| by means of a pair of rivets |21 and |28 whichextend through openings in the bracket 99, the base 35, the bracket ||3,the xed core member ||1 v and elongated slots |29 in a movable coremember |23 hereinafter described. The rivets |21 and |28 have centrallylocated heads |3| which abut against the lower face of the bracket H9,and the upper ends of the rivets are peened over to rigidly secure thebrackets 99 and I9 to the base 55 of the trip device. The lower ends ofthe rivets |21 and |28 are provided with spacers |33 (Fig. 4) and |34,respectively, having reduced portions abutting against the fixed coremember and firmly held thereagainst. The spacers |33 and |34 are alsoprovided with flanged portions of a larger diameter than the width ofthe slots |23 of the adjustable core member to retain the movable coremember |23 in place but which permit adjusting movement of the coremember |23. The reduced portion of the spacer |34 on the rivet (Fig. 3)is made longer than the reduced portion of the spacer |33 to accommodatea bell crank lever |35 which is pivotally mounted thereon. One arm |31of the bell crank lever carries a pin |39 which projects into anelongated slotin the movable core member |23 whereby movement of thelever |35 is transmitted to the movable core member |23 to move itrelative to the fixed core member I|1 and also relative to the armature|25. The other arm I4| of the bell crank lever extends parallel to andjust inside the bottom of the cover |00 of the trip device. The free endof the arm |4| is formed at right angles to the the bell crank |35 andthe movable core member |28 in the adjusted position.

I'he armature |25 is threadedly mounted on one end of a horizontallydisposed trip rod |5| and is locked in place by a set screw |53. The rodI5| is slidably mounted in a formed over portion |55 of the non-magneticbracket Il! and the armature is held in retracted position against thebracket by means of a spring |51 compressed between the portion |55 ofthe bracket and a nut |53 threadedly engaging an enlarged and threadedmid portion of the rod |5I. At its right-hand Aend (Figs. 2 and 3) therod I5| projects through an open slot |6| in the trip bar and isprovided .with a head |55 which, upon movement of the armature toattracted position engages and operates the trip .bar to trip theinterrupter.

The movable core member |23 is of the same` general U-shape as the fixedcore member ||1 and lies iiat against the lower face of the fixed coremember. When the movable core member |23 is in its position closest tothe armature |25, the pole faces oi the two core members aresubstantially in line. The movable core member provides a path for aportion of the magnetic flux parallel to the magnetic iiux path throughthe xed core member. The magnetic flux through the armature |25 and boththe fixed and movable core members produces a pull on the .armaturetending to move it in tripping direction. The initial air gap betweenthe armature |25 and the core member |1 is fixed but the air gap betweenthe movable core member |23 and the armature may be varied by adjustingthe position of the movable core member in the previously describedmanner. This varies the over-all pull on the armature produced by bothcore members.

The ends of the movable core member |23 are formed over at right anglesand lie adjacent the ends of the fixed core member. Each formedoverportion of the movable or adjustable core member |23 is provided with anarm |63 which arms extend to the right (Fig. 3) and are formed inwardlytoward each other. The purpose of the arms |63 is to provide a limitedpath for at least .a portion of the magnetic flux and thereby provide adifferential pull on the armature |25 which may be varied according tothe adjust` ment of the core member I 23. The ends of the armature |25and of the core means IIT-|23 are slanted inwardly along av lineextending toward the center of U of the core means. This not onlyincreases the pole face area and thereby provides for maximum pull onthe low trip setting where the current is low but also provides a corneron the armature of relatively small area facing the parallel extensionsof the core member |23 so that the lateral iiux leakage to the parallelextensions is reduced and there is a strong back pull between theinturned arms |63 on the extensions and the back of the armature |25,

Referring to the lower portion of Fig. 3, it may be seen that theinstantaneous magnetic tripping means -for the right-hand pole of theinterrupter is adjusted to trip in response to overload currents of highvalue. In this adjusted position the adjustable core member |23 has beenmoved to the left away from the armature and way from the pole faces ofthe fixed core member ||1, thus differentially increasing theA air gapof the magnet and decreasing the pull-of theA magnet for a given amountof current.- Movement of the adjustable core member |23l also moves thebent arms |53 thereof closer' to the outer side of the armature. themovement oi' the member |23 in this direction being limited by the arms|33 ensains the portion |55 of the non-magnetic bracket ||3 (Fig. 2). Inthis position there is a slight air gap between the arms |83 and theright-hand face of the amature |25. In the adjustment oi the trip devicejust described, the inward pull of the magnetic core members and |23 onthe amature in tripping direction is differentially decreased and theback pull of the arms |63 is increased for a given value of overloadcurrent.. When the bell crank lever |25 is rotated clockwise from thehigh" position toward the low" position, the adjustable core member |23ismoved toward the armature |25 and the arms |63 are moved away from thearmature. This has the eiIect oi' decreasing the magnetic air gap andincreasing the pull of'the magnet on the amature in tripping direction.Also, as the arms |83 move away from the armature, the back pull on thearmature opposing tripping movement thereof decreases so that when thedevice is set at a position below the highest position which it iscapable of adjustment, the trip device will be actuated in response tooverloads of lesser magnitude to trip the interrupter.

By way oi' example, assuming that the breaker is rated to carry a normalload indenitely without actuating the trip device, the bimetal may becalibrated to trip the breaker with an inverse time delay in response tooverloads of say between 100% and 300% of the normal rated current. Theelectromagnetic trip device may be calibrated and adjusted toinstantaneously trip the breaker on overloads of, for instance, between300% and 1100% of rated current depending on the setting of the lever|35 and the corresponding adjustment of the movable core member |23.Assuming that the trip device is calibrated to the above arbitraryvalues, then with the device set to the low" position, as shown in theupper part oi' Fig. 3, the electromagnet will operate to instantaneouslytrip the breaker upon the occurrence of an overload current of 300% ormore of normal. If the lever |35 is moved to the high position tocorrespondingly adjust the movable core member |23, the armature willnot 'be attracted until the occurrence of an overload current of 1100%of normal. By adjusting the lever |35 to any point between the maximumand minimum settings, the magnet will function to instantaneously tripthe breaker in response to an overload current of a minimum valuecorresponding to the particular setting ofthe device. Thus the devicemay be set to cause instantaneous tripping of the breaker in response toa minimum overload of, for instance, 300%,A

500% or 700%, etc., up to 1100% of normal rated current. It will beunderstood that if the device is adjusted to instantaneously trip out ata minimum overload of, for instance, 700% of normal, the bimetal element|05 will function to trip the breaker after a time delay upon theoccurrence of overload currents of any value between 100% and 700%, orbetween 100% and the particular minimum current value between 300% and1100% to which the magnet is adiusted.

The time delay tripping may be adjusted by rotating the screw |09 in thetrip b ar to vary the distance of theend of the screw from the bi'-metal element. Y

The high instantaneous trip setting is determined by the small air gapbetween the amature |25 and the arms |63 of the movable core mem-'- 8ber.andbytheairgapbctweenthemovablecorc member |23 and the armature. Thelow in- .stantaneous trip setting is determined by the initial force ofthe spring |51. The initial tension ot the spring |51 may be varied byturning the nut |53 on the threaded portion of the rod |5| to increaseor decrease the tension oi' the spring. This varies the lowinstantaneous tripping current required to trip the breaker when theadjustable magnet core is set to the low position.

From the foregoing description, it will be seen that the inventionprovides a circuit breaker having an improved trip device wherein theelectromagnetic trip means is provided with two parallel magnetic fluxcircuits and corresponding air gaps disposed to produce a differentialpull on the armature so that a wide range of adjustment is obtained, theminimum current value required to trip the breaker being selectivelydetermined by varying the air gaps to thereby vary the differentialmagnetic pull on the armature.

While the invention has been disclosed in accordance with theprovisionsof the patent statutes, it is to be understood that various changes inthe structural details and arrangement of parts thereof may be madewithout departing from some oi the essential features of the invention.It is desired, therefore, that the language of the appended claims begiven as reasonably broad interpretation as the prior art permits.

We claim as our invention:

1. In a circuit interrupter, tripping means including electromagneticmeans comprising an armature and ilxedly mounted magnetic core means, aunitary movable magnetic core means movable relative to said amature andhaving portions disposed on each side of said amature to cause saidelectromagnet to produce a differential pull on said armature. and meanstor adjusting said movable core means relative to said armature to varythe din'erential pull o! said electromagnet to thereby selectivelydetermine the minimum value of overload current required to operate saidarmature.

2. In a circuit interrupter the combination of an armature operable toeffect automatic operation of said interrupter, electromagnetic meanscomprising a fixed main pole structure cooperating with said armatm-e todenne a main air. gap an auxiliary pole structure disposed adjacent saidfixed pole structure and movable relative to said nxed pole structureand said armature to vary the main magnetic air gap between saidarmature and said pole structure, means integral with said auxiliarypole structure providing a back drag on said armature, said integralmeans being movable with said auxiliary pole structure to vary the backdrag on said armature, and means for adjusting said auxiliary polestructure and said integral means to selectively determine the trippingcharacteristic oi' said electromagnetic means.

3. In a circuit interruptor, the combination of a tripping armature, anenergizing winding traversed by the current of the circuit of theinterrupter, a main pole structure comprising a tlxedly mounted mainpole member and a unitary auxiliary pole member cooperating with saidmain pole member to produce a forward pull on said armature and movablerelative to said main pole member and said armature, said auxiliary polemember having a part disposed to cause said pole structure to produce aback pull on said armature, and manual means for moving said auxiliary:,soaive pole member relative to said main pole member and said armatureto vary the magnetic air gap between the armature and said main polestruc. ture and to simultaneously vary the back pull of said polestructure'.

4. In a circuit interrupter, an armature, electroresponsive meanscomprising a pole structure including a main pole member fixedly mountedin front of said armature defining a main air gap, a unitary auxiliarypole member slidably mounted in front of said armature adjacent to saidmain pole member` and` movable relative thereto to vary the main air gapof said electromagnet, said auxiliary pole member having portionsintegral therewith disposed to cause said pole structure to produce aback pull on said armature, said pole structure being effective whenenergized in response to overload currents above a predeterminedmagnitude to operate said armature, and means for adjustably positioningsaid auxiliary pole member and said integral portions relative to saidmain pole member and said armature to selectively determine themagnitude of the current required to instantaneously operate saidarmature.

5. In a circuit interrupter, an armature, electromagnetic meansenergized in response to the current in the circuit of the interrupterfor operating said armature, said electromagnetic means comprising axedly mounted main pole member disposed in front of said armaturedelining a main air gap, an auxiliary pole member disposed in front ofsaid armature and movable relative to said main pole member to vary themain air gap of the electromagnetic means, means integral with saidauxiliary pole member disposed back of said armature to produce a back.drag on said armature, said integral means being movable with saidauxiliary pole member to vary the back drag on said armature.

6. An electroresponsive device comprising an energizing winding, anarmature cooperating therewith, a xedly mounted pole member cooperatingwith said armature to define a main air gap, a movably mounted auxiliarypole member cooperating with said xedly mounted pole member to produce aforward pull on said armature, means on said auxiliary pole memberdisposed to produce a back drag on said armature, said auxiliary polemember and said means together being movable to vary the main air gap ofthe electroresponsive device and to vary the back drag on said armature.

7. The combination of an energizing winding. an armature cooperatingtherewith, a pole structure comprising a main ixedly mounted polestructure and an auxiliary pole structure movable relative to said mainpole structure, said main pole structure and said auxiliary polestructure cooperating to produce a forward pull on said armature, meansmounted on and movable with said auxiliary pole structure for causingsaid pole structure to produce a diiferential pull on said armature, andmeans for selectively adjusting said auxiliary pole structure.

8. An electromagnet comprising an energizing winding, a movablearmature, a fixedly mounted main pole member disposed adjacent one sideof said armature, a movable pole member mounted adjacent said xedlymounted pole member and movable relative thereto, said pole membersproducing a forward pull on said armature, means on said movable polemember and disposed adjacent the opposite side of said armature forproducing a back drag on said armature, said pole members overcomingsaid back drag and operating said armature when energized in response tocurrent of a predeterminedl magnitude traversing said winding, andmanual means for adjusting said movable pole member to selectivelydetermine the magnitude of current required to operate said armature.

9. An electroresponsive device comprising an energizing winding, anarmature cooperating therewith, a U-shaped pole member mounted on afixed support 'and cooperating with said arma@ ture to define a main airgap, a slidablymounted U-shaped auxiliary pole member disposed` adjacentto said ilxedly mounted pole member and cooperating therewith to producea forward pull on said armature, projections on said auxiliary polemember cooperating with said armature to produce a back drag thereon,said 'auxiliary pole member and said projections being movable relativeto said fixedly mounted pole member and said armature to vary the mainair gap of said electroresponsive device and to vary the back drag onsaid armature.

l0. In a circuit interrupter, an electromagnet comprising an armature, aU-shaped magnetic core operable in response to overload currents toeffect operation of said armature, said core having a portion disposedin front of said armature, said U-shaped core having pole faces at theends thereof slanting inwardly toward the center of the U and havingsubstantially parallel extensions at the outer edges of the U extendingbeyond said slanting pole faces, said extensions having at the outerends thereof inwardly directed portions extending in back of the endportions of the armature, said armature having slanting faces adjacentto and cooperating with the slanting pole faces on the core, and saidslanting faces of the armature terminating in a corner at each end ofthe armature of small area for reducing the lateral ux leakage to saidextensions and enhancing the back pull and a portion disposed back ofsaid armature to produce a differential pull on said armature, andmanual means for effecting relative movement between said armature andboth portions of said core to vary the differential pull of saidelectromagnet.

11. In a circuit interrupter comprising operating means for causingautomatic operation of said interrupter, an electromagnet comprising anarmature, a core member having portions arranged in relation to saidarmature to provide a main air gap on one side of said armature and asecondary air gap on the opposite side of said armature, a core havingan extension beyond the end of the armature and having pole portionspositioned oppositely on each side of the armature to provide a main airgap on one side of the armature and a secondary air gap on the otherside of the armature producing a differential pull on the armature, thepole portion for one of said air gaps being slanted at an angle relativeto the i polel portion of the other air gap, said armature having aslanting end portion facing said slanting pole portion and providing anend of reduced section for reducing the lateral flux leakage to saidextension of the core, producing a differential `pull on said armature,and manual means for effecting relative movement between said armatureand said core member to vary both of said .air gaps to thereby vary thedifferential pull on u electromagnetic means operable in response to 11overload currents to effect automatic opening of said contact means.said electromagnetic means including an amature, a xed core member, a

.movable core member cooperative with said xed core member to produce aforward pull on said armature to operatesaid amature, a portion integralwith said movable core member disposed and arranged to cause saidelectromagnetic means to produce a differential pull on said armature,and adjusting means for selectively positioning said movable core memberand said integral portion relative to said armature to vary thedinerential pull to thereby selectively determine the minimum overloadcurrent value required to operate said armature.

EURE LINDBTROM.

BmYARD Qi.

REFERENCES crrlm The foiiovving references are oi record in the ie of.this patent:

UNITED STATES PATENTS Number Name Date Re. 18,683 Y Scott Dec. 6. 1933130.795 Edison Aug. 27, 1872 685,431 Pearson Oct. 29. 1901- 1,227,341Stratton May 22, 1917' 2,044,133 Stolz et ai. June .18. 1936 2.047,73?ly Liugai July 14. 193#I

